Topics

IRCS First Light !

June 16, 2000

May was a busy month at Subaru Telescope, with the resumption
of commissioning after repairing the detached fixed point (see
our May 12
"Topics" ) and the release of the first Call
for Proposals inviting astronomers from Japan and elsewhere to
use the Subaru Telescope for their own research.

Two instruments, Suprime-Cam
and IRCS,
are being offered for Open Use operation, and this month we focus
on IRCS, the Infrared
Camera and Spectrograph.
As its name suggests, IRCS is able to take both images and spectra
in the wavelength range of 1-5 microns. It can image at longer
wavelengths than OHS,
and over a wider field of view than CIAO.
It also offers higher resolution spectroscopy than either of these
two instruments. Its versatility is expected to make it one of
the most popular instruments on Subaru Telescope.

IRCS saw first light on the night of 25 February, mounted at
the Cassegrain focus
of the telescope for a total of 6 nights. Since then, the data
gathered has been analyzed to see where adjustments need to be
made.

Although most of the observations taken by IRCS earlier this
year were intended to test the instrument's performance, IRCS
has already obtained important scientific results from its observations
of the gamma
ray burst GRB 000301C.

Many of the most interesting places in the Universe, such as
regions where stars are forming or the centres of galaxies, are
hidden behind large amounts of dust. They can only be seen in
detail at wavelengths longer than 2.5 microns, where the dust
is less efficient at absorbing light. IRCS is designed to work
efficiently at these long wavelengths, which are known as the
"thermal infrared". Objects at the ambient temperature
(e.g., the telescope) emit large amounts of heat radiation at
these wavelengths.

When IRCS is used in its spectroscopy mode, it breaks infrared
light up into its component infrared "colors". One of
the important things we can do with spectroscopy is measure the
velocity of objects out in space. CIAO and OHS, which use dispersing
elements called "grisms", can only provide a course
measure of the motions of objects, unable to sense differences
smaller than a few hundred kilometres per second. IRCS also contains
grisms to perform course observations; but in addition, it contains
an "echelle", which can disperse light much more finely.
IRCS can detect differences in relative motions as small as 15
km/s, suitable for detailed studies of the gases within objects
ranging from young stars to entire galaxies. [For comparison,
note that objects at the equator of the Earth are travelling at
0.46 km/s (1037 mph) due to the Earth's rotation and the Earth
is moving at about 30 km/s due to its orbital motion about the
Sun.]

IRCS will be mounted on the telescope several more times during
the remainder of this year for further testing, including some
using the Adaptive
Optics unit which arrived in Hilo last month. Among other
projects, the IRCS team hopes to use their instrument to search
for brown dwarfs (''failed stars'' with masses 10-100 times that
of Jupiter), investigate chemical reactions around stars, and
study the dynamics of distant galaxies.

After initial testing in Japan, OHS was dismantled and transported
to Hawaii. It was reassembled at the IR Nasmyth focus of Subaru
Telescope and underwent further tests before receiving first light.